Signal to notify gradle selection

Change-Id: Ie9db0ca4b4133e63f06cda8fe9f3be8080eeaae9
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/android/androidbuildapkstep.cpp

@@ -262,9 +262,12 @@ bool AndroidBuildApkStep::useGradle() const
 
 void AndroidBuildApkStep::setUseGradle(bool b)
 {
+    if (m_useGradle != b) {
         m_useGradle = b;
         if (m_useGradle)
             AndroidManager::updateGradleProperties(target());
+        emit useGradleChanged();
+    }
 }
 
 bool AndroidBuildApkStep::runInGuiThread() const

src/plugins/android/androidbuildapkstep.h

@@ -81,6 +81,9 @@ public:
     virtual Utils::FileName androidPackageSourceDir() const = 0;
     void setDeployAction(AndroidDeployAction deploy);
 
+signals:
+    void useGradleChanged();
+
 protected:
     Q_INVOKABLE void showInGraphicalShell();